Start-reversing vertical screw elevator

ABSTRACT

A conveyor is disclosed for granular or pulverulent materials which comprises a vertically disposed screw elevator rotatable within a casing and a specially constructed receptacle at the inlet end of the casing for receiving material deposited when the direction of rotation of screw is reversed to free compacted material in the casing.

United States Patent [191 UNITED STATES PATENTS 2,357,220 li/ 1944 Qlson l98/2l3 H Schmidth Nov. 13, 1973 [54] START-REVERSING VERTICAL SCREW 2,232,545 2/1941 Lum 198/213 2,045,757 6/1936 Constantin... 198/123 ELEVATOR 3,633,718 1/1972 Wanner 198/110 [75] Inventor: Claus A. Schmidth, 3,300,032 1/1967 Dion 198/213 Copenhagen-Valby, Denmark [73] Assignee: F. L. Smidth 8!. C0., Cresskill, NJ. Primary Examiner-Edward A. Sroka D S. Ed (1 t 1. 221 Filed: Mar. 22, 1972 can s e a 0M v 2 w. 2... 57 ABSTRACT [30] Foreign Application Priority Data A conveyor 15 disclosed for granular or pulverulent Apr. 14, 1971 Great Britain 9395/71 I materials which comprises a vertically disposed screw elevator rotatable within a casing and a specially con- [52] US. Cl. 198/213, 222/ 195 structed receptacle at the inlet end of the casing for [51] Int. Cl. B65g 33/14, B67d 5/06 receiving material deposited when the direction of ro- [58] Field of Search 198/64, 110, 213; tation of screw is reversed to free compacted material 222/195; 214/83, 32; 302/50 in the casing.

[56] References Cited I Claims, 4 Drawing Figures STAR'IQREVERSING VERTICAL SCREW ELEVATOR BACKGROUND OF THE INVENTION The present invention is concerned with screw elevators for granular or pulverulent materials, the elevatorcomprising at least one conveyor screwwhich is rotated in an enclosed casing having a bottom inlet for the material to be conveyed and an outlet at its upper end.

Elevators of this kind are frequently used for the substantially vertical transport of pulverulent material, such as cement raw meal or cement, because of their simple and space-saving construction and their ability to transport such material at a controlled rate to appreciable heights.

The elevators are often used in continuous operations in which reliable performance of the elevator is of the utmost importance. However, in such installations stoppage of the elevators may occur for one reason or other and if the elevator is stopped for some period, perhaps due to a failure of the current supply, the material may form a compacted mass in the casing, making start up of the screw conveyor difficult or even blocking its re-start totally.

In order to bring the elevator into condition for a start again it is then necessary to open the casing and to remove at least part of the compacted material. This is a troublesome and time-wasting procedure and accounts for the fact that screw elevators are not used as much as would otherwise be desirable in installations for a continuous production or treatment of a material, such as in the production of cement.

SUMMARY OF THE INVENTION In accordance with the present invention, an improved screw elevator is provided in which the above disadvantages are substantially avoided. In construction, the screw elevator is provided with means for driving the screw conveyor for a short period in the reverse direction before it is started up in the normal direction of transport. The bottom of the casing is provided with a receptacle for accommodating surplus material carried down by the conveyor screw during the initial reverse drive period.

By reversing the conveyor screw for a short period, usually only a few revolutions of the conveyor screw being sufficient, the compacted mass'of material in the casing is broken up so that the screw may be started in the proper direction without difficulties. However, the reversal involves some of the material accommodated in the casing being transported back downwards and in order to make room for this material the bottom of the conveyor casing is provided with a receptacle of a suitable size for receiving this material, which otherwise would be compacted in the bottom of the casing and possibly give rise to further trouble.

In the preferred construction, the bottom of the casing has means for fluidizing the material to be transported. The fluidization of the material helps especially to distribute the material transported backwards into the receptacle but it improves also the regular transport of the material by the screw elevator after the re-start.

The starting of the screw elevator may be regulated by hand, but preferably the re-start is controlled automatically, for example by a time-lag relay and a revolution counter which registers the number of revolutions of the screw conveyor. The reverse starting of the screw elevator can thus be carried out in the shortest possible time, thus reducing to a minimum the amount of material returned to the receptacle, as it is only necessary to ensure that the number of reverse revolutions are just sufficient to break up the compacted mass. Should the reverse speed of the screw or its rate of acceleration from reverse to forward drive become too high, all the material in the casing may slide down to the bottom. Preferably therefore, the means for driving the conveyor screw operate at a lower speed during the reverse drive of the conveyor than during the subsequent normal drive and the time-lag relay is arranged in the start circuit to block the start of the screw conveyor in the transport direction until the screw conveyor has reached a standstill.

Often such elevator installations are duplicated by the installation of two or more co-operating conveyor screws to increase the capacity of the elevator and to have a standby unit. When the elevator comprises more than one screw conveyor the conveyor screw casings preferably have a common bottom part containing weir plates for separating the receptacles for the conveyor screws.

The bottom part of the casing serving one conveyor screw may thereby act as a receptacle for material transported backwards when an adjacent conveyor screw is reversed before it is started. It is then superfluous to introduce separate receptacles for each conveyor screw for receiving material returned during the initial start of the conveyor screw.

At the same time this arrangement is advantageous for ensuring that material is present in the bottom of the conveyor casing when a conveyor screw is started, which is important as the material load is necessary to provide protection of the conveyor screw bearings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical section through a conveyor with one screw;

FIG. 2 is part of a vertical section through a conveyor with two screws;

FIG. 3 is a side view of the conveyor shown in FIG. 2; and,

FIG. 4 is a diagram of the electric connections for a conveyor motor.

DETAILED DESCRIPTION OF THE INVENTION As shown in FIG. 1, the elevator comprises a casing 1 of circular cross-section. The casing hasan inlet 2 for material and an outlet 3 at its top and contains a conveyor screw 4 rotatable in the casing by means of an electric motor and a reduction gear coupled to a coupling part 5 of the top of the screw conveyor but not shown in the drawing. The bottom of the tubular casing 1 is equipped with a material reception box 6 the bottom of which has a false bottom 7 for introducing fluidizing air into the casing. Fluidizing air is admitted to the casing through a pipe connection 8.

FIG. 2 shows the lower part of a vertical elevator comprising two conveyor screws 10 and 11 in a casing 12 with two separate inlets 13 and 14 for material and means in the form of a false bottom 15 for distributing fluidizing air into the casing and thereby fluidizing the material. The air is introduced through a pipe 16. The lower ends of the two conveyor screws are separated by a weir plate 17.

With reference now to FIG. 4, the electric motor driving a conveyor screw is designated 20. The motor is connected to the main supply through a contactor 21 by means of which the direction of the rotation of the motor may be reversed by interchanging two phases. The contactor is operated by means of two coils 22 and 23 which receive their working current through a control box 24 containing interlocking relays which insure that only one of the coils 22, 23 can operate the contactor at a time and time-lag relays, so that a reversal of the motor is made at standstill of the motor. An impulse indicator 25 may be set to stop the motor after a certain number of revolutions of the screw in the direction reverse to the normal direction for transport of material.

When the conveyor screw is stopped, for instance due to failure of the power supply, the casing l is normally partly filled with material being transported whereas the bottom of the casing has only a material level sufficient to feed the vertical conveyor screw. Frequently the material feed to the vertical elevator is regulated according to a level measurement in the bottom of the conveyor casing by means of a suitable indicator which may regulate the feed or a conveyor screw feeding material to the vertical elevator.

In case the stoppage of the elevator is for a considerable period of time the material in the casing 1 will compact to a more or less solid mass, making the start of the conveyor screw impossible or difficult with mechanical damage of the conveyor as a result. By reversing the conveyor screw a few revolutions the compacted mass is loosened and the start of the conveyor screw in the proper direction for transport of material may then more easily be carried out.

Upon the reversing operation at least part of the material in the casing is forced to the bottom of the casing where it is accommodated in the receptacle 6. The material is fluidized by means of air injected through the false bottom 7, most of it being removed again when the conveyor screw is started in the proper direction.

In the example shown in FIGS. 2 and 3 and comprising a double elevator, of which one of the conveyor screws may serve as a stand-by unit, the bottom casing for one conveyor screw may act also as a receptacle for material returned when the other conveyor screw is reversed. By means of the fluidizing air introduced into the casing through the false bottom 15, the material flows over the weir 17.

It is important to insure that the screw, after having been reversed, is at a standstill before being started again in the direction of transport. This is accomplished by introducing a time-lag relay in the control box 24, interlocking the operation of the two coils 22 and 23.

The impulse indicator 24 counts the number of revolutions of the conveyor screw when this is reversed and is preset to stop the reversing according to requirements. It is important to keep the reversing of the conveyor screw at a minimum in order not to compact all the material present in the conveyor casing in the bottom of the casing.

I claim:

1. A screw elevator for granular or pulverulent material, the elevator comprising at least one conveyor screw mounted for rotation within an enclosed casing having a bottom inlet for material to be conveyed and an outlet at its upper end, and means for driving each screw conveyor for a short period in the reverse direction before it is started up in the normal direction of transport, the bottom of the casing being provided with (1) a receptacle for accommodating surplus material carried down by the conveyor screw during the initial reverse drive period and (2) means for fluidizing surplus material accumulated therein whereby distribution of material transported back into said receptacle during said reverse drive period and transportation of material during said normal drive period is enhanced.

2. An elevator according to claim 1 including two or more conveyor screws mounted for rotation within said casing and further including one or more weir plates separating the common bottom part of said easing into a seperate receptacle for each of said screws.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Inventor-(s) Claus A s hmidth It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column L line 12, change indicator 2b." to read indicator 2S v-.

Signed and sealed this 21st day of May 1971;.

(SE L) Attest Tim-FARE) I-Ll IJJTCHBZQ'JH. v 8 MAI-(SHALL DANN Attesting fficer Commissioner of Patents FORM PC4050 (10-69) UscMM Dc Os-764,69

V U.S. GOVERNMENT PRINTING OFFICE l9! O3 -38l. 

1. A screw elevator for granular or pulverulent material, the elevator comprising at least one conveyor screw mounted for rotation within an enclosed casing having a bottom inlet for material to be conveyed and an outlet at its upper end, and means for driving each screw conveyor for a short period in the reverse direction before it is started up in the normal direction of transport, the bottom of the casing being provided with (1) a receptacle for accommodating surplus material carried down by the conveyor screw during the initial reverse drive period and (2) means for fluidizing surplus material accumulated therein whereby distribution of material transported back into said receptacle during said reverse drive period and transportation of material during said normal drive period is enhanced.
 2. An elevator according to claim 1 including two or more conveyor screws mounted for rotation within said casing and further including one or more weir plates separating the common bottom part of said casing into a seperate receptacle for each of said screws. 